SBVS064O December   2005  – October 2024 TPS74201

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Enable and Shutdown
      2. 6.3.2 Power-Good (VQFN Packages Only)
      3. 6.3.3 Internal Current Limit
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Dropout Operation
      3. 6.4.3 Disabled
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Input, Output, and Bias Capacitor Requirements
      2. 7.1.2 Transient Response
      3. 7.1.3 Dropout Voltage
      4. 7.1.4 Output Noise
      5. 7.1.5 Programmable Soft-Start
      6. 7.1.6 Sequencing Requirements
    2. 7.2 Typical Applications
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
      3. 7.4.3 Thermal Protection
      4. 7.4.4 Thermal Considerations
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Evaluation Modules
        2. 8.1.1.2 Spice Models
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
      2. 8.2.2 Device Nomenclature
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.1.5 Programmable Soft-Start

The TPS742 devices feature a programmable, monotonic, voltage-controlled soft start that is set with an external capacitor (CSS). This feature is important for many applications, because power-up initialization problems are eliminated when powering FPGAs, DSPs, or other processors. The controlled voltage ramp of the output also reduces peak inrush current during start-up, minimizing start-up transients to the input power bus.

To achieve a linear and monotonic soft-start, the TPS742 error amplifier tracks the voltage ramp of the external soft-start capacitor until the voltage exceeds the internal reference. The soft-start ramp time depends on the soft-start charging current (ISS), soft-start capacitance (CSS), and the internal reference voltage (VREF), and can be calculated using Equation 2:

Equation 2. TPS74201

If large output capacitors are used, the device current limit (ICL) and the output capacitor can set the start-up time. In this case, the start-up time is given by Equation 3:

Equation 3. TPS74201

VOUT(NOM) is the nominal set output voltage as set by the user, COUT is the output capacitance, and ICL(MIN) is the minimum current limit for the device. In applications where monotonic start-up is required, the soft-start time given by Equation 2 must be set to be greater than Equation 3.

The maximum recommended soft-start capacitor is 0.015 μF. Larger soft-start capacitors can be used and do not damage the device; however, the soft-start capacitor discharge circuit is not always able to fully discharge the soft-start capacitor when enabled. Soft-start capacitors larger than 0.015 μF can be a problem in applications where the user must rapidly pulse the enable pin and still requires the device to soft-start from ground. CSS must be low-leakage; X7R, X5R, or C0G dielectric materials are preferred. See Table 7-1 for suggested soft-start capacitor values.

Table 7-1 Standard Capacitor Values for Programming the Soft-Start Time
(See Equation 4)
CSSSOFT-START TIME
Open0.1 ms
470 pF0.5 ms
1000 pF1 ms
4700 pF5 ms
0.01 μF10 ms
0.015 μF16 ms
Equation 4. TPS74201

where

  • tSS(s) = soft-start time in seconds